The Internet Protocol (IP) multimedia subsystem (IMS), defined by the 3rd Generation Partnership Project (3GPP), is an architectural framework for implementing IP-based telephony and multimedia services. IMS defines a set of specifications that enable the convergence of voice, video, data and mobile technology over an all IP-based network infrastructure. In particular, IMS fills the gap between the two most successful communication paradigms—cellular and Internet technology, by providing Internet services everywhere using cellular technology in a more efficient way. Session Initiation Protocol (SIP) is the main protocol for IMS. SIP is an application layer control (signaling) protocol for creating, modifying and terminating sessions (e.g., voice sessions) with one or more participants.
A Voice over Long Term Evolution (VoLTE) network is based on the IMS network and provides IP-based voice and data service via a network complying with the LTE standard. VoLTE has more voice and data capacity than many other wireless networks, while using less available bandwidth due to the use of smaller packet headers.